BOS has self-tagging, both on the 'normal' area and the SkyPriority side of the ticketing counters. However, they rarely have the yellow Priority tags at the kiosks, so if you want one you have to take your bag tag and have the agent put it on with a priority tag. Also if you have a tight connection you still would want an agent to put the red and yelow 'Rapid Transfer' tag or whatever its called.

Last I was there a couple weeks ago, it is still agent-assisted... pax can check in and print out the bag tags but you still had to get in line for bag drop with an agent.
I hate using the kiosk anyway since half the time they don't work right or are slower than going to the SP agent assist line.